1. Field of the Invention
This invention relates to decay-resistant paper for the manufacture of a pot for raising and transplanting seedlings, which is characterized in that it partly contains decayable portions, and to an improved process for easily producing the same.
2. Description of the Prior Art
The method of cultivating plants by raising and transplanting of seedlings by the use of a pot of four- or six-cornered cylinder without lid and bottom (or with a bottom), which is made of a film of paper or the like, has been expensively employed.
In this plant cultivation method, and above-described pot is filled with culture soil, seeds are sowed therein, the seedlings are grown under controlled applying of water, and the pot is planted in a field. After the transplantation, the pot gradually breaks in the field as a result of decay, thereby allowing free extension of roots out of the pot walls.
However, the decay of the pot after transplantation depends strongly on the properties of the soil; when the decay is slow, said free extension of roots may be obstructed, thus delaying the plant growth of the beginning stage.
Accordingly, the paper used for the manufacture of a pot for raising and transplanting of seedlings is required to have a sufficiently high strength under dry conditions (tear strength) to be proof against mechanical handling during the pot manufacture (folding and stretching), to have a sufficiently high strength under wet conditions to be proof against artificial and mechanical handling during raising and transplanting of seedlings, and to show a high degree of breakage after transplantation regardless of the properties of soil, thus breaking rapidly to allow free extension of roots.
In recent years, various kinds of paper for the manufacture of a pot for raising and transplanting seedlings having the properties described above have been proposed. For example, Japanese Patent Laid-Open No. 35138/'74 disclosed a process for producing decay-resistant paper partly containing decayable portions, which is characterized in that, when making decay-resistant paper by treating the pulp cellulose with a reagent capable of crosslinking and hindering the hydroxyl groups in cellulose (such as formaldehyde), a water-repellent compound, such as paraffin, is previously attached to the paper surface in the pepper-and-salt or polka-dotted form, thereby partly preventing the crosslinking between cellulose and the reagent and hindering reactions between the hydroxyl groups and the reagent. Japanese Patent Laid-open No. 501317/'85, and the corresponding U.S. Pat. No. 4,610,761, disclosed a process for producing decay-resistant paper partly containing decayable portions, which is characterized in that, when making paper decay-resistant by treating the paper with an N-methylol compound, a compound containing carboxyl groups is previously attached to the paper surface in preset portions, thereby preventing antidecaying treatment in these portions.
These prior arts are characterized in that a water-repellent compound (such as paraffin) or a compound containing carboxyl groups is attached to the paper surface in preset portions prior to antidecay treatment of the paper. However, it is practically very difficult to attach any of these compounds correctly according to the desired pattern. In addition, attachment of a water-repellent compound without any flow and penetration of a compound containing carboxyl groups only in the desired portions involve the problems to be solved, because the processing rate is restricted, thereby lowering the production efficiency and raising the production cost.